The process of creating a vapor from a liquid can be accomplished by heating the liquid to a sufficiently high temperature to cause the liquid to undergo a phase change and become a vapor. To generate vapor at a sufficiently high rate, it is necessary to supply an adequate amount of heating energy to the liquid in a relatively short time. This can be accomplished by increasing the operating temperature of the vapor generating apparatus or providing a larger heat transfer surface so that heat can be conducted more easily into the liquid.
In semiconductor applications, a wide variety of precursor chemicals are available in liquid form for vapor generation and for subsequent thin film deposition on a substrate by a vapor phase process. Processes such as chemical vapor deposition (CVD), plasma-enhanced chemical vapor deposition (PECVDP), metal-organic CVD (MOCVD), atmosphere pressure chemical vapor deposition (APCVD) and atomic layer deposition (ALD) are well known to those skilled in the art of semiconductor device fabrication. Some precursor chemicals such as metal-organic compounds can decompose at high temperatures to form undesirable by-products to cause process or equipment contamination. For such applications, the heating temperature must be kept low to avoid thermal decomposition and by-product formation. Increasing the heat transfer surface area will generally cause the overall physical size of the apparatus to increase, thus making the device less responsive to changing vapor demands in the process. The response speed of the apparatus will thus decrease. As a result, the traditional approach to increasing vaporization rate is not suitable for all applications.